Integrating transmissive LCD's high contrast ratio and good color saturation and reflective LCD's low power consumption, transflective LCD is viewable at anytime and anywhere. Transflective LCD is an emerging display technology with wide application including mobile displays and communication displays, like mobile phone, barcode scanners, gaming, global positioning system (GPS)/navigation devices, personal data assistant (PDA), e-books, and the like.
A transflective LCD is disclosed in U.S. Pat. Nos. 6,281,952 B1 to Okamoto et al.; 6,295,109 B1 to Kudo et al.; 6,330,047 B1 to Kubo et al., using a split-pixel approach, i.e. each pixel is split into reflective (R) and transmissive (T) sub-pixels. Usually, the R and T area ratio is 4:1, in favor of reflective display mode in order to conserve power. The transmissive region with small area ratio is used for dark ambient surroundings only.
Two types of transflective LCDs have been developed: single cell gap 100 type as shown in FIG. 1 and double cell gap 200 type as shown in FIG. 2. In the single cell gap type, the cell gap 100 of the T-region is substantially equal to that of the R-region, which leads to the same response time in both T and R regions; however, their electro-optical curves cannot overlap well because light passes through the T-region once but through the R-region twice.
In the double cell gap approach, the cell gap 200 of the T-region and that of the R-region have approximately two times the difference so that the response time has approximately four times the difference between the R-region and the T-region. The split-pixel approach, regardless of whether single or double cell gap, has complicated structures and fabrication processes since each pixel is divided into R and T sub-pixels. Thus, the double cell gap LCD is more complicated than the single cell gap LCD.
In U.S. Pat. No. 6,124,971 to Ouderkirk et al., assigned to 3M Innovative Properties Company, a transflective structure is provided, using a reflective polarizing transflector, as shown in FIG. 3. The structure in FIG. 3 is a single cell gap 300 approach without split-pixel, thus, it is easy to fabricate. However, the transflector is located between the polarizer and backlight source, which results in parallax (double image) and deteriorates the resolution. In U.S. Pat. No. 4,093,356 to Bigelow, assigned to the General Electric Company, a transflective LCD with a metallic mirror 400 is described and shown in FIG. 4. The transflector is a half-silver metallic mirror, which is quite thin (˜50 nm) so that it can crack easily. The transflective LCD designs provided by both the 3M inventors and the General Electric inventor suffer from parallax. Parallax is that double image with displacement that occurs when one views a display panel from an oblique angle. Thus, it is desirable to have a parallax-free, transflective LCD that is robust, easy and inexpensive to fabricate.